3-(6-isobutyl-9-methoxy-1-4-dioxo-1-2-3-4-6-7-12-12a-octahydropyrazino(1--2--1-6)pyrido(3-4-b)indol-3-yl)propionic-acid-tert-butyl-ester and Glioblastoma

Over-expression of both P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP) has been associated with multidrug-resistance in glioblastoma (GBM). Though previously studied broad-spectrum inhibitors of drug efflux pumps have failed to progress in clinical studies due to in vivo toxicity, research into clinically viable targeted inhibitors is needed. This study evaluated the effects of Ko143, a non-toxic analog of fumitremorgin C, on temozolomide (TMZ) efficacy in resistant glioblastoma stem cells.. We used ATP-Glo assay to determine cell viabilities and flow cytometry to perform cell cycle analysis. Comparative gene expression was analysed through RT-qPCR.. TMZ IC. Further development of non-toxic, targeted inhibitors of drug efflux pumps for use in combinatorial chemotherapy may improve glioblastoma patient prognosis.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily G, Member 2; Cell Line, Tumor; Cell Survival; Diketopiperazines; Drug Resistance, Neoplasm; Drug Synergism; Glioblastoma; Heterocyclic Compounds, 4 or More Rings; Humans; Neoplasm Proteins; Temozolomide

Photodynamic therapy (PDT) of malignant brain tumors is a promising adjunct to standard treatment, especially if tumor stem cells thought to be responsible for tumor progression and therapy resistance were also susceptible to this kind of treatment. However, some photosensitizers have been reported to be substrates of ABCG2, one of the membrane transporters mediating resistance to chemotherapy. Here we investigate, whether inhibition of ABCG2 can restore sensitivity to photosensitizer chlorin e6-mediated PDT.. Accumulation of chlorin e6 in wild type U87 and doxycycline-inducible U251 glioblastoma cells with or without induction of ABCG2 expression or ABCG2 inhibition by KO143 was analyzed using flow cytometry. In U251 cells, ABCG2 was inducible by doxycycline after stable transfection with a tet-on expression plasmid. Tumor sphere cultivation under low attachment conditions was used to enrich for cells with stem cell-like properties. PDT was done on monolayer cell cultures by irradiation with laser light at 665nm.. Elevated levels of ABCG2 in U87 cells grown as tumor spheres or in U251 cells after ABCG2 induction led to a 6-fold lower accumulation of chlorin e6 and the light dose needed to reduce cell viability by 50% (LD50) was 2.5 to 4-fold higher. Both accumulation and PDT response can be restored by KO143, an efficient non-toxic inhibitor of ABCG2.. Glioblastoma stem cells might escape phototoxic destruction by ABCG2-mediated reduction of photosensitizer accumulation. Inhibition of ABCG2 during photosensitizer accumulation and irradiation promises to restore full susceptibility of this crucial tumor cell population to photodynamic treatment.

Topics: ATP Binding Cassette Transporter, Subfamily G, Member 2; Cell Line, Tumor; Cell Survival; Chlorophyllides; Diketopiperazines; Doxycycline; Gene Expression; Glioblastoma; Heterocyclic Compounds, 4 or More Rings; Humans; Light; Niacinamide; Phenylurea Compounds; Photosensitizing Agents; Porphyrins; Sorafenib

Despite multimodal treatment that includes surgery, radiation and chemotherapy, virtually all glioblastomas (GBM) recur, indicating that these interventions are insufficient to eradicate all malignant cells. To identify potential new therapeutic targets in GBMs, we examined the expression and function of proteins that are associated with therapy resistance and cancer cell survival. We measured the expression of eight such proteins in 50 GBM samples by immunohistochemistry and analyzed patient survival. We report that GBM patients with high expression of ABCG2 (also called BCRP) or XIAP at the protein level had worse survival than those with low expression. The adjusted hazard ratio for ABCG2 was 2.35 and for XIAP was 2.65. Since glioma stem cells (GSCs) have been shown to be more resistant than bulk tumor cells to anti-cancer therapies and to express high levels of these proteins, we also sought to determine if ABCG2 and XIAP have functional roles in GSCs. We used small molecule inhibitors to treat patient-derived GBM tumorspheres in vitro and observed that inhibitors of ABCG2, Ko143 and fumitremorgin, significantly reduced self-renewal. These results suggest that ABCG2 and XIAP proteins may be useful indicators of patient survival and that inhibition of ABCG2 may be a promising therapeutic strategy in GBMs.

Topics: Adult; Aged; Aged, 80 and over; Animals; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 2; Brain Neoplasms; Cells, Cultured; Dacarbazine; Diketopiperazines; Female; Follow-Up Studies; Glioblastoma; Heterocyclic Compounds, 4 or More Rings; Humans; Indoles; Male; Mice, Inbred NOD; Mice, Knockout; Mice, SCID; Middle Aged; Neoplasm Proteins; Neoplasm Transplantation; Neoplastic Stem Cells; Temozolomide; X-Linked Inhibitor of Apoptosis Protein